A thief has been slicing open the pockets of sleeping straphangers in Brooklyn since February, and police are now asking the public’s help catching him.

Police released video of alleged thief Wednesday, linking him to seven thefts on the southbound L train since Feb. 16.

The suspected pocket slasher prowled the subway cars between midnight and 5 a.m., stealing wallets and cellphones from riders as they dozed.

Police describe the suspect as black, between 30 and 40 years old, between 5-foot-8 and 6 feet tall, and about 180 to 190 pounds. He was last seen wearing a light blue button-down shirt, a Yankees hat, blue jeans and black sneakers.

Cops are asking anyone with information to call Crime Stoppers at (800) 577-TIPS.